The Met Office has warned that a Sudden Stratospheric Warming (SSW) is now highly likely to occur which is likely to affect UK weather at the end of the month.
The weather forecasting organisation has issued a detailed explanation of the impact that such warming trends high up in the atmosphere can have on weather in the UK but said it is not as simple as meaning that we will be hit by heavy snowfall and cold weather.
A Sudden Stratospheric Warning describes an event when rapid warming occurs high up in the stratosphere - the second layer of the atmosphere immediately above the troposphere, which is closest to Earth. It refers to an area between 10km to 50km above the earth's surface and its effects are not usually felt until several weeks later.
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SSW's are often thought to lead to widespread snow and cold temperatures in the UK but not always. For example, the SSW in February 2018 led to the ‘Beast from the East’ whereas the SSW in January 2019 had no significant impact for the UK weather. So while the rest of February is expected to be frosty, this is not necessarily all down to events high above us.
In a detailed blog explaining the weather trend, the forecaster wrote that the chance of a stratospheric warming was now at 80% but it was not certain that the warming would affect the jet stream - the powerful air currents crossing the Atlantic which have a huge impact on UK weather.
The forecaster wrote: ""A major SSW often makes the jet stream meander more, which can lead to a large area of blocking high pressure over northern Europe, including the UK. This blocking high pressure can lead to cold, dry weather in the north of Europe, including the UK, with mild, wet and windy conditions more likely for southern areas of the continent. However, this is not always the case and impacts on UK weather can also be benign when an SSW occurs."
The current extended range forecast for mid-February suggests that the most likely scenario is for broadly changeable weather with westerly conditions and influxes of wind and rain at times, particularly in the northwest. Temperatures are likely to be around average through mid-February.
Prof Adam Scaife, Head of Long-Range Forecasting at the Met Office, said: “There is now over 80% chance of a major SSW occurring. Although the impact will become clearer nearer the time, any effect on UK weather is most likely to occur in late February and March.”
Other factors can also impact the UKs weather in winter such as the Madden Julian Oscillation which is now also tracking towards a state that favours a cooler spell in late February.
The UK long range weather forecast from February 12 to February 21:
"Sunday and Monday will be mostly dry with variable and at times large amounts of cloud, with any fog patches clearing through the morning. Parts of the north and northwest of the UK will remain rather damp at times, with occasional light rain or drizzle. Over the following few days, probably a gradual transition to more generally changeable conditions, meaning a greater chance of some rain at times in the south and east compared to earlier in February.
"The north and northwest will likely be most unsettled, with often strong winds accompanying periods of rain, which will be heavy at times. Temperatures overall will be relatively mild, with any frost mostly likely across southern areas earlier in the period."
From February 22 to March 7:
"During the period, generally settled weather conditions are expected across the UK. Frontal systems bringing rain and strong winds are expected in the northwest, perhaps spreading further into the southeast at times, although much of the south and southeast may stay largely dry. Temperatures overall will be above normal, with a small but increasing chance of colder conditions as we move through the period."
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